Upgrade mdev to allow commands to be run on create/delete.

Both Jason Schoon and Giuseppe Ciotta deserve credit for this, I used elements
of both.  It's been upgraded so that you can specify that a given command
should run at create, at delete, or at both using different special characters
(@, $, and * respectively).  It uses the system() method of running command
lines which means you can use environment variables on the command line (it
sets $MDEV to the name of the current device being created/deleted, which is
useful if you matched it via regex), and the documentation warns that you need
a /bin/sh to make that work, so you probably want to pick a default shell.

3 files changed, 130 insertions, 105 deletions

diff --git a/include/usage.h b/include/usage.h
index 8defbd1fc..712eede63 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -1799,19 +1799,25 @@ USE_FEATURE_DATE_ISOFMT( \
         "\t-s\tScan /sys and populate /dev during system boot\n\n" \
         "Called with no options (via hotplug) it uses environment variables\n" \
         "to determine which device to add/remove."
-#ifdef CONFIG_FEATURE_MDEV_CONFIG
-#define mdev_notes_usage \
+#define mdev_notes_usage "" \
+USE_FEATURE_MDEV_CONFIG( \
         "The mdev config file contains lines that look like:\n" \
         "  hd[a-z][0-9]* 0:3 660\n\n" \
         "That's device name (with regex match), uid:gid, and permissions.\n\n" \
-        "Optionally, that can be followed (on the same line) by an asterisk\n" \
-        "and a command line to run after creating the corresponding device(s),\n"\
-        "ala:\n\n" \
-        "  hdc root:cdrom 660  *ln -s hdc cdrom\n\n" \
+        USE_FEATURE_MDEV_EXEC( \
+                "Optionally, that can be followed (on the same line) by a special character\n" \
+                "and a command line to run after creating/before deleting the corresponding\n" \
+                "device(s).  The environment variable $MDEV indicates the active device node\n" \
+                "(which is useful if it's a regex match).  For example:\n\n" \
+                "  hdc root:cdrom 660  *ln -s $MDEV cdrom\n\n" \
+                "The special characters are @ (run after creating), $ (run before deleting),\n" \
+                "and * (run both after creating and before deleting).  The commands run in\n" \
+                "the /dev directory, and use system() which calls /bin/sh.\n\n" \
+        ) \
         "Config file parsing stops on the first matching line.  If no config\n"\
         "entry is matched, devices are created with default 0:0 660.  (Make\n"\
-        "the last line match .* to override this.)\n\n"
-#endif
+        "the last line match .* to override this.)\n\n" \
+)
 
 #define mesg_trivial_usage \
         "[y|n]"
diff --git a/util-linux/Config.in b/util-linux/Config.in
index a493fbfb4..501ed6bfc 100644
--- a/util-linux/Config.in
+++ b/util-linux/Config.in
@@ -265,16 +265,31 @@ config CONFIG_FEATURE_MDEV_CONF
 
           That's device name (with regex match), uid:gid, and permissions.
 
-          Optionally, that can be followed (on the same line) by an asterisk
-          and a command line to run after creating the corresponding device(s),
-          ala:
-
-            hdc root:cdrom 660  *ln -s hdc cdrom
-
           Config file parsing stops on the first matching line.  If no config
           entry is matched, devices are created with default 0:0 660.  (Make
           the last line match .* to override this.)
 
+config CONFIG_FEATURE_MDEV_EXEC
+        bool "Support command execution at device addition/removal"
+        default n
+        depends on CONFIG_FEATURE_MDEV_CONF
+        help
+          This adds support for an optional field to /etc/mdev.conf, consisting
+          of a special character and a command line to run after creating the
+          corresponding device(s) and before removing, ala:
+
+            hdc root:cdrom 660  *ln -s $MDEV cdrom
+
+          The $MDEV environment variable is set to the name of the device.
+
+          The special characters and their meanings are:
+            @ Run after creating the device.
+            $ Run before removing the device.
+            * Run both after creating and before removing the device.
+
+          Commands are executed via system() so you need /bin/sh, meaning you
+          probably want to select a default shell in the Shells menu.
+
 config CONFIG_MKSWAP
         bool "mkswap"
         default n
diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index 73a82314c..3c7cf7bd1 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -8,25 +8,14 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
 
+#include "busybox.h"
 #include <ctype.h>
-#include <dirent.h>
 #include <errno.h>
-#include <fcntl.h>
-#include <stdio.h>
-#include <string.h>
 #include <sys/mman.h>
-#include <sys/stat.h>
 #include <sys/sysmacros.h>
-#include <sys/types.h>
-#include <unistd.h>
-#include <stdlib.h>
-#include "busybox.h"
 #include "xregex.h"
 
 #define DEV_PATH        "/dev"
-#define MDEV_CONF       "/etc/mdev.conf"
-
-#include <busybox.h>
 
 struct mdev_globals
 {
@@ -36,14 +25,15 @@ struct mdev_globals
 #define bbg mdev_globals
 
 /* mknod in /dev based on a path like "/sys/block/hda/hda1" */
-static void make_device(char *path)
+static void make_device(char *path, int delete)
 {
-        char *device_name, *s;
+        char *device_name;
         int major, minor, type, len, fd;
         int mode = 0660;
         uid_t uid = 0;
         gid_t gid = 0;
         char *temp = path + strlen(path);
+        char *command = NULL;
 
         /* Try to read major/minor string.  Note that the kernel puts \n after
          * the data, so we don't need to worry about null terminating the string
@@ -69,7 +59,7 @@ static void make_device(char *path)
                 char *conf, *pos, *end;
 
                 /* mmap the config file */
-                if (-1 != (fd=open(MDEV_CONF,O_RDONLY))) {
+                if (-1 != (fd=open("/etc/mdev.conf",O_RDONLY))) {
                         len = lseek(fd, 0, SEEK_END);
                         conf = mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);
                         if (conf) {
@@ -86,88 +76,89 @@ static void make_device(char *path)
                                                 ;
 
                                         /* Three fields: regex, uid:gid, mode */
-                                        for (field=3; field; field--) {
+                                        for (field=0; field < (3 + ENABLE_FEATURE_MDEV_EXEC);
+                                                        field++)
+                                        {
                                                 /* Skip whitespace */
-                                                while (pos<end && isspace(*pos))
-                                                        pos++;
-                                                if (pos==end || *pos=='#')
-                                                        break;
-                                                for (end2=pos; end2<end && !isspace(*end2) && *end2!='#'; end2++)
+                                                while (pos<end && isspace(*pos)) pos++;
+                                                if (pos==end || *pos=='#') break;
+                                                for (end2=pos;
+                                                        end2<end && !isspace(*end2) && *end2!='#'; end2++)
                                                         ;
 
-                                                switch (field) {
+                                                if (!field) {
                                                         /* Regex to match this device */
-                                                        case 3:
-                                                        {
-                                                                char *regex = strndupa(pos,end2-pos);
-                                                                regex_t match;
-                                                                regmatch_t off;
-                                                                int result;
-
-                                                                /* Is this it? */
-                                                                xregcomp(&match,regex,REG_EXTENDED);
-                                                                result = regexec(&match,device_name,1,&off,0);
-                                                                regfree(&match);
-
-                                                                /* If not this device, skip rest of line */
-                                                                if (result || off.rm_so || off.rm_eo!=strlen(device_name))
-                                                                        goto end_line;
 
+                                                        char *regex = strndupa(pos, end2-pos);
+                                                        regex_t match;
+                                                        regmatch_t off;
+                                                        int result;
+
+                                                        /* Is this it? */
+                                                        xregcomp(&match,regex, REG_EXTENDED);
+                                                        result = regexec(&match, device_name, 1, &off, 0);
+                                                        regfree(&match);
+
+                                                        /* If not this device, skip rest of line */
+                                                        if (result || off.rm_so
+                                                                        || off.rm_eo != strlen(device_name))
                                                                 break;
-                                                        }
+
+                                                } else if (field == 1) {
                                                         /* uid:gid */
-                                                        case 2:
-                                                        {
-                                                                char *s2;
-
-                                                                /* Find : */
-                                                                for(s=pos; s<end2 && *s!=':'; s++)
-                                                                        ;
-                                                                if (s == end2)
-                                                                        goto end_line;
-
-                                                                /* Parse UID */
-                                                                uid = strtoul(pos,&s2,10);
-                                                                if (s != s2) {
-                                                                        struct passwd *pass;
-                                                                        pass = getpwnam(strndupa(pos,s-pos));
-                                                                        if (!pass)
-                                                                                goto end_line;
-                                                                        uid = pass->pw_uid;
-                                                                }
-                                                                s++;
-                                                                /* parse GID */
-                                                                gid = strtoul(s,&s2,10);
-                                                                if (end2 != s2) {
-                                                                        struct group *grp;
-                                                                        grp = getgrnam(strndupa(s,end2-s));
-                                                                        if (!grp)
-                                                                                goto end_line;
-                                                                        gid = grp->gr_gid;
-                                                                }
-                                                                break;
+
+                                                        char *s, *s2;
+
+                                                        /* Find : */
+                                                        for(s=pos; s<end2 && *s!=':'; s++)
+                                                                ;
+                                                        if (s == end2) break;
+
+                                                        /* Parse UID */
+                                                        uid = strtoul(pos,&s2,10);
+                                                        if (s != s2) {
+                                                                struct passwd *pass;
+                                                                pass = getpwnam(strndupa(pos, s-pos));
+                                                                if (!pass) break;
+                                                                uid = pass->pw_uid;
+                                                        }
+                                                        s++;
+                                                        /* parse GID */
+                                                        gid = strtoul(s, &s2, 10);
+                                                        if (end2 != s2) {
+                                                                struct group *grp;
+                                                                grp = getgrnam(strndupa(s, end2-s));
+                                                                if (!grp) break;
+                                                                gid = grp->gr_gid;
                                                         }
+                                                } else if (field == 2) {
                                                         /* mode */
-                                                        case 1:
-                                                        {
-                                                                mode = strtoul(pos,&pos,8);
-                                                                if (pos != end2)
-                                                                        goto end_line;
-                                                                else
-                                                                        goto found_device;
+
+                                                        mode = strtoul(pos, &pos, 8);
+                                                        if (pos != end2) break;
+                                                } else if (ENABLE_FEATURE_MDEV_EXEC && field == 3) {
+                                                        // Command to run
+                                                        char *s = "@$*", *s2;
+                                                        if (!(s2 = strchr(s, *pos++))) {
+                                                                // Force error
+                                                                field = 1;
+                                                                break;
                                                         }
+                                                        if ((s2-s+1) & (1<<delete))
+                                                                command = bb_xstrndup(pos, end-pos);
                                                 }
+
                                                 pos = end2;
                                         }
-end_line:
+
                                         /* Did everything parse happily? */
-                                        if (field && field!=3)
-                                                bb_error_msg_and_die("Bad line %d",line);
+
+                                        if (field > 2) break;
+                                        if (field) bb_error_msg_and_die("Bad line %d",line);
 
                                         /* Next line */
                                         pos = ++end;
                                 }
-found_device:
                                 munmap(conf, len);
                         }
                         close(fd);
@@ -175,13 +166,29 @@ found_device:
         }
 
         umask(0);
-        if (mknod(device_name, mode | type, makedev(major, minor)) && errno != EEXIST)
-                bb_perror_msg_and_die("mknod %s failed", device_name);
+        if (!delete) {
+                if (mknod(device_name, mode | type, makedev(major, minor)) && errno != EEXIST)
+                        bb_perror_msg_and_die("mknod %s failed", device_name);
 
-        if (major==bbg.root_major && minor==bbg.root_minor)
-                symlink(device_name, "root");
+                if (major == bbg.root_major && minor == bbg.root_minor)
+                        symlink(device_name, "root");
         
-        if (ENABLE_FEATURE_MDEV_CONF) chown(device_name, uid, gid);
+                if (ENABLE_FEATURE_MDEV_CONF) chown(device_name, uid, gid);
+        }
+        if (command) {
+                int rc;
+                char *s;
+                
+                s=bb_xasprintf("MDEV=%s",device_name);
+                putenv(s);
+                rc = system(command);
+                s[4]=0;
+                putenv(s);
+                free(s);
+                free(command);
+                if (rc == -1) bb_perror_msg_and_die("Couldn't run %s", command);
+        }
+        if (delete) unlink(device_name);
 }
 
 /* Recursive search of /sys/block or /sys/class.  path must be a writeable
@@ -212,7 +219,7 @@ static void find_dev(char *path)
 
                 /* If there's a dev entry, mknod it */
 
-                if (!strcmp(entry->d_name, "dev")) make_device(path);
+                if (!strcmp(entry->d_name, "dev")) make_device(path, 0);
         }
 
         closedir(dir);
@@ -247,12 +254,9 @@ int mdev_main(int argc, char *argv[])
             if (!action || !env_path)
                         bb_show_usage();
 
-                if (!strcmp(action, "add")) {
-                        sprintf(temp, "/sys%s", env_path);
-                        make_device(temp);
-                } else if (!strcmp(action, "remove")) {
-                        unlink(strrchr(env_path, '/') + 1);
-                }
+                sprintf(temp, "/sys%s", env_path);
+                if (!strcmp(action, "add")) make_device(temp,0);
+                else if (!strcmp(action, "remove")) make_device(temp,1);
         }
 
         if (ENABLE_FEATURE_CLEAN_UP) RELEASE_CONFIG_BUFFER(temp);